1. Field of the Invention
The invention relates to a stent-like structure which in one embodiment can be used for treating neurovascular or brain aneurysms.
2. Description of Related Art
A stent is a tubular structure that in a radially compressed state (crimped state) may be inserted into a vessel in the body. Once located in the vessel, the stent may be expanded radially to a predefined size (expanded state). Stents are typically characterized as balloon expanding or self expanding. A balloon expanding stent requires a balloon, which is part of the delivery system, to expand the stent from the crimped state to an expanded state. A self expanding stent is designed, through choice of material, geometry, or manufacturing techniques, to expand from a crimped state to an expanded state once the stent is released into the intended vessel.
A stent is commonly thought of as a device that opens a narrowed artery. A stent-like structure has similar characteristics to a stent, but may not open or support an artery. Unless otherwise indicated, as used hereafter, the term “stent” will be understood to encompass both a stent and stent-like structure.
An aneurysm is a weakened area in a vessel that has expanded or bulged. Untreated aneurysms are susceptible to rupture. Stenting of an aneurysm could strengthen the weakened vessel by cutting off significant blood flow to the aneurysm. The reduced blood flow could result in thrombosis in the aneurysm and promote healing regardless of the aneurysm form or shape. Stents have been used to treat aneurysms. Conventional stent grafts have been used to treat Thoracic and Abdominal Aortic Aneurysms. Stent grafts have a metallic stent structure covered by graft material. Stents have also been used experimentally to repair neurovascular aneurysms which were first treated with platinum coils that have migrated over time into the parent vessel. See Pride, Jr. et al., Endovascular problem solving with intravascular stents, AJNR Am J Neuroradiol. 2000; 21:532-540.
One system, Boston Scientific's Neuroform Microdelivery Stent System, is described for use with embolic coils. Conventional treatment includes aneurysm clipping, which requires a craniotomy, or aneurysm coiling, placing small platinum or polymer coils in the aneurysm to facilitate thrombosis. The above-described conventional methods for treatment of neurovascular aneurysms have certain drawbacks. Coiling is effective when the aneurysm has a well defined neck (transition from the bulging portion of the vessel to the nominal vessel diameter). If this neck transition is wide or long, coiling is not as effective as the coils tend to migrate and cause other complications, as described in Lownie et al., Endovascular therapy of a large vertebral artery aneurysm using stent and coils, Can J Neurol Sci 2000; 27:162-165 and Wanke et al., Treatment of wide-necked intracranial aneurysms with a self-expanding stent system: initial clinical experience, AJNR Am J Neuroradiol. 2003; 24:1192-1199. Clipping is very invasive, risky and expensive.
Current coronary stents typically have an expandable “Z” strut scaffolding structure that allows efficient radial expansion and effective vessel dilation. This type of structure requiring a large open area is not expected to be effective for treating neurovascular aneurysms because the large open areas would not inhibit blood flow. In coronary stents, radial expansion is achieved by opening the scaffolding structure to produce a structure that is mostly open area. Coronary stents typically have 75% to 90% open area (10 to 25% vessel coverage).
It is believed that in order for stenting to be effective for treating brain aneurysms, the percent of the vessel covered would need to be at least about 35%. It is desirable to provide a stent for treating neurovascular or brain aneurysms having the percent of the vessel covered of at least about 35%.